1. Field of the Invention
2. Discussion of the Background
FIGS. 9 and 10 are respectively a perspective view and an exploded perspective view of a magnetic head suspension of a conventional type. As illustrated in these figures, a magnetic head suspension 100 of the conventional type includes, a flexure 110 having a stainless-steel substrate 111 for mounting a magnetic head slider (not illustrated) thereon and a wiring structure 112 integrally formed on the said stainless-steel substrate 111, a load beam 120 with a load-bent portion for generating a force to press the magnetic head slider against a magnetic disk, and a base plate 130 for securing the magnetic head suspension to an arm (not illustrated), in which these component parts are welded together.
The wiring structure 112 of the flexure 110 includes a terminal pad 113 closer to the slider positioned at a distal end portion of the flexure wiring, a terminal pad 115 closer to the base plate positioned at a proximal end portion of the flexure, and a signal line portion 114 extending between said terminal pads closer to the slider and the base plate. While the terminal pad 113 closer to the slider is connected to a terminal of the magnetic head slider, the terminal pad 115 closer to the base plate is connected to a terminal of a relay FPC 140 that is, in turn, connected to a preamplifier IC.
In the recent tendency towards application of a MR head to a magnetic head, an MR device is used as a reading device, and an inductive device is used as a writing device. This arrangement usually needs the flexure wiring 120 with four wires (two for reading and two for writing).
FIGS. 11(a) and 11(b) are respectively vertical cross sections of a wiring integrated flexure of a general type, the former being a cross section of the signal line portion 114 of the wiring structure 112 of the flexure, the latter a cross section of the terminal pad 113 or 115 of the wiring structure 112.
As illustrated in FIG. 11(a), a portion of the flexure 110 corresponding to the signal line portion 114 includes a stainless-steel substrate 111, a polyimide insulating layer 116 laminated on the said stainless-steel substrate 111, a Cu-wiring-conductor layer 117 laminated on the said insulating layer, and a polyimide protection layer 118 covering the said wiring conductor layer. Usually, the polyimide insulating layer 116 and the Cu-wiring-conductor layer 117 respectively have a thickness of 5 to 10 xcexcm and a thickness of 5 to 10 xcexcm, while the polyimide protection layer 118 has a thickness of 1 to 3 xcexcm on the wiring conductor layer. On the other hand, the terminal pads 113 and 115 of the wiring structure 112 of the flexure each define an opening 118a in the polyimide insulating layer 118, through which the wiring conductor layer 117 is exposed.
In the above arrangement, polyimide used for the insulating layer 116 and the protection layer 118 has a different coefficient of thermal expansion from stainless steel. In addition, polyimide exhibits a moisture-absorption property. These factors may cause the variation of the mechanical characteristic, specifically the variation of the angle or the attitude angle of a slider-mounting region 111b of a gimbal portion 111a with regard to the load beam (see FIGS. 9 and 10). Therefore, the thinner polyimide insulating layer and polyimide protection layer can stabilize the mechanical characteristics of the flexure.
On the other hand, when giving consideration to the electrical characteristics of the wiring structure, the thinner polyimide insulating layer is likely to be influenced by Eddy current flowing through the stainless-steel substrate, thereby disadvantageously increasing the resistance in the wiring structure. This increase in resistance of the wiring structure becomes more remarkable as the signal frequency becomes higher. The increase in the resistance of the wiring structure causes signals transmitting through the wiring structure to further decay, thereby hardly accomplishing a high-speed data transmission. In addition, the thinner polyimide insulating layer increases the capacitance between the wiring structure and the stainless-steel substrate. Such an increase in capacitance lowers the resonance frequency of a circuit system including a wiring structure and a magnetic head, where the length of the wiring structure is sufficiently short with regard to the signal wavelength. As a result, it is hard to read high-speed signals from and write the same to the magnetic disk.
Such increases in resistance and capacitance of the wiring structure accompanied by the thinner polyimide insulating layer can effectively be limited by selectively removing the portions of the stainless-steel substrate present below the wiring structure. Specifically, the capacitance in the wiring structure can be reduced by arranging opening portions below the wiring structure in the stainless-steel substrate. However, such opening portions greatly deteriorate the flexibility in mechanical designing of the flexure.
U.S. Pat. No. 5,739,982 discloses a flexure with the wiring conductor partly positioned sidewards of the stainless-steel substrate so as to limit the increase in resistance and capacitance of the wiring structure. This arrangement, however, poses a problem that the portion of the wiring conductor sidewards of the stainless-steel substrate is likely to be damaged or deformed by any other parts or matters, which are easily accessible to the wiring conductor sideways. As an additional problem in the flexure disclosed in the said U.S. patent publication, protrusions extending sidewards from the stainless-steel substrate for supporting the wiring conductor positioned sidewards of the stainless-steel substrate may deteriorate the flexibility in mechanical designing of the flexure.
The present invention has been conceived to solve these problems. It is an object of the invention to provide a wiring integrated flexure that is capable of avoiding deterioration of the flexibility in mechanical designing of the flexure, decreasing influences of the insulating layer over the mechanical characteristics of the flexure, and reducing resistance and capacitance of the wiring structure.
It is another object of the invention to provide a method of manufacturing such a wiring integrated flexure.
In accordance with the present invention, there is provided a wiring integrated flexure including a stainless-steel substrate for supporting a magnetic head slider thereon, a wiring conductor formed on the said stainless-steel substrate, posts made of a flexible resin and interposed between the stainless-steel substrate and the wiring conductor for electrically isolating the wiring conductor from the stainless-steel substrate, and the posts disposed along the lengthwise direction of the wiring conductor with spacing from each other.
The wiring integrated flexure of the above arrangement can achieve a reduction in capacitance in the wiring structure, prevention of the increase in resistance of the wiring structure in a high frequency signal region. In addition, the contacting area between the flexible resin and the stainless-steel substrate can be reduced so that the mechanical characteristics of the flexure is unlikely to be deteriorated, thereby providing an wiring integrated flexure having stabilized mechanical characteristics. Those effects are obtainable without defining openings in a region of the stainless-steel substrate below the wiring conductor, so that the flexibility in mechanical designing of the flexure is unlikely to be deteriorated. Further, the wiring conductor is not located sidewards of the stainless-steel substrate, but located within the stainless-steel substrate, so that any other parts or matters are unlikely to contact the wiring conductor from the lateral side or the lower side. Therefore, it is possible to effectively prevent the wiring conductor from being damaged or deformed.
The wiring integrated flexure preferably includes a base bottom layer made of a flexible resin and provided between each post and an adjacent post thereto of the posts in contact with a bottom surface of the wiring conductor and with spacing from the stainless-steel substrate.
The base bottom layer for supporting the wiring conductor in cooperation with the posts can achieve improved mechanical strength of the wiring conductor, resulting in improved reliability of the wiring structure.
The wiring conductor preferably has an outer surface covered with an Au layer.
The wiring conductor preferably has an outer surface covered with a protection layer made of a flexible resin.
The protection layer can achieve protection of the wiring conductor from the outside air, resulting in improved reliability of the wiring structure
The wiring conductor preferably includes a protection pattern that is formed on the stainless-steel substrate extending along both the longitudinal sides of the stainless-steel substrate with the wiring conductor there between.
The protection pattern can reduce the load on the posts effected by a possible contact with any matters from above the flexure, and therefore preventing the wiring conductor from being damaged or deformed.
As another aspect of the invention, there is provided a method of manufacturing a wiring integrated flexure including a stainless-steel substrate for supporting a magnetic head slider thereon, a wiring conductor formed on the said stainless-steel substrate, posts made of polyimide and interposed between the stainless-steel substrate and the wiring conductor for electrically isolating the wiring conductor from the stainless-steel substrate, and the posts disposed along the lengthwise direction of the wiring conductor with spacing from each other, which includes:
a first step of applying a polyimide precursor onto the entire surface of the stainless-steel substrate;
a second step of curing the polyimide precursor by prebaking to form a polyimide precursor layer;
a third step of forming a wiring conductor pattern on the polyimide precursor layer;
a forth step of forming resists on regions of the polyimide precursor layer to be respectively formed into the posts, and the wiring conductor pattern;
a fifth step of etching out the polyimide precursor layer by using the resists as masks; and
a sixth step of modifying the polyimide precursor layer left on the stainless-steel substrate into a polyimide layer by heat treatment.
The method of manufacturing a wiring integrated flexure further includes a step of forming an Ni/Au layer on the surface of the wiring conductor layer by electrolytic plating between the third step and the forth step, said third step including:
forming a build-up-forming conductive layer formed of a Cr layer on the entire surface of the polyimide precursor layer;
forming a plating resist on the build-up-forming conductive layer with the exception of a region thereof corresponding to the wiring conductor pattern;
forming an Au/Ni/Cu containing wiring conductor layer on the exposed surface of the build-up-forming conductive layer by electrolytic plating by using the plating resist as a mask;
removing the plating resist and the build-up-forming conductive layer with the exception of a region thereof, in which the wiring conductor layer has been formed; and
As still another aspect of the invention, there is provided a method of manufacturing a wiring integrated flexure including a stainless-steel substrate for supporting a magnetic head thereon, a wiring conductor formed on the said stainless-steel substrate, posts made of polyimide and interposed between the stainless-steel substrate and the wiring conductor for electrically isolating the wiring conductor from the stainless-steel substrate, the posts disposed along the lengthwise direction of the wiring conductor with spacing from each other, and a base bottom layer made of polyimide and formed between each post and an adjacent post thereto of the posts in contact with a bottom surface of the wiring conductor and with spacing from the stainless-steel substrate, which includes:
a first step of applying a negative photosensitive polyimide onto the entire surface of the stainless-steel substrate;
a second step of curing the negative photosensitive polyimide by prebaking to form a photosensitive polyimide layer;
a third step of exposing the entire thickness of post forming regions of the negative photosensitive polyimide layer to light, the said post forming regions respectively corresponding to the posts;
a forth step of exposing only a surface side of a base-bottom-layer forming region of the photosensitive polyimide layer to light, the said base-bottom-layer forming region corresponding to the base bottom layer and including at least a region corresponding to the wiring conductor layer;
a fifth step of developing the photosensitive polyimide layer and subsequently subjecting the same to heat treatment so as to leave the entire thickness of the post forming regions of the photosensitive polyimide layer and the surface side of the base-bottom-layer forming region of the photosensitive polyimide layer located between adjacent posts of the posts, as a polyimide layer so as to form the posts and the base bottom layer;
a sixth step of forming a resist defining openings therein open to the posts and the base bottom layer;
a seventh step of depositing a Cr/Cu-containing build-up-forming conductive layer on the entire surface by sputtering, after forming the resist;
an eighth step of removing the resist so as to leave the build-up-forming conductive layer only on the posts and the base bottom layer;
a ninth step of forming a first plating resist defining an opening therein open to a region of the build-up-forming conductive layer, the said region corresponding to the wiring conductor;
a tenth step of forming a Cu-containing conductor layer on a region of the build-up-forming conductive layer exposed via the opening of the first plating resist, by electrolytic plating;
an eleventh step of removing the first plating resist and the build-up-forming conductive layer with the exception of the region thereof on which the Cu-containing conductor layer has been formed; and
a twelfth step of forming a second plating resist on a region with the exception of the posts and the base bottom layer, and forming an Ni/Au layer on the Cu-containing conductor layer by electrolytic plating.
As another aspect of the invention, there is provided a method of manufacturing a wiring integrated flexure including a stainless-steel substrate for supporting a magnetic head thereon, a wiring conductor formed on the said stainless-steel substrate, a protection layer made of polyimide and covering the surface of the said wiring conductor, posts made of polyimide and interposed between the stainless-steel substrate and the wiring conductor for electrically isolating the wiring conductor from the stainless-steel substrate, the posts disposed along the lengthwise direction of the wiring conductor with spacing from each other, and a base bottom layer made of polyimide and formed between each post and an adjacent post thereto of the posts in contact with a bottom surface of the wiring conductor and with spacing from the stainless-steel substrate, which comprises:
a first step of forming on the stainless-steel substrate a first resist with openings therein respectively open to post-forming regions, the said post-forming regions respectively corresponding to the posts;
a second step of applying a polyimide precursor on the entire surface of the first resist and regions of the stainless-steel substrate exposed via the openings, and forming a first polyimide precursor layer by prebaking;
a third step of forming a second resist on post forming regions and a base-bottom-layer forming region of the polyimide precursor, the post forming regions respectively corresponding to the posts, and the base-bottom-layer forming region corresponding to the base bottom layer;
a fourth step of etching out the exposed portion of the polyimide precursor layer by using the second resist as a mask;
a fifth step of etching out the second resist and depositing a build-up-forming conductive layer entirely on the first polyimide precursor layer left on the stainless-steel substrate and the exposed surface of the first resist by sputtering;
a sixth step of forming a plating resist on the build-up-forming conductive layer with the exception of a region thereof corresponding to the wiring conductor;
a seventh step of forming a wiring conductor layer on the exposed surface of the build-up-forming conductive layer by electrolytic plating by using the plating resist as a mask;
an eighth step of removing the plating resist and etching out the exposed portion of the build-up-forming conductive layer by using the wiring conductor layer as a mask;
a ninth step of applying a polyimide precursor entirely on the exposed surface of the first resist, the exposed surface of the first polyimide precursor and the wiring conductor layer in such a manner as to cover the wiring conductor layer, and forming a second polyimide precursor layer by prebaking;
a tenth step of forming a third resist on a region of the second polyimide precursor layer, the said region corresponding to the posts and the base bottom layer;
an eleventh step of etching out the exposed portion of the second polyimide precursor layer by using the third resist as a mask, and leaving only a portion of the second polyimide precursor layer, the said portion covering the wiring conductor; and
a twelfth step of removing the first resist and the third resist, and subjecting the first polyimide precursor layer and the second polyimide precursor layer left on the stainless-steel substrate to heat treatment to modify the first polyimide precursor layer and the second polyimide precursor layer respectively into polyimide layers so as to form the posts, the base bottom layer and the protection layer.